We calculate the strength of the electroweak phase transition in a supersymmetric model with four chiral generations. The additional chiral fermions (and scalar partners) lower the critical temperature and thus strengthen the first-order phase transition. The scalar partners stabilize the potential, leading to an effective theory that is bounded from below. We identify the ensemble of parameters where ${\varphi }_c/T_c\gtrsim 1$ simultaneous with obtaining a large enough Higgs mass. Our calculations focus on a subset of the full four generational supersymmetric parameter space: We take the pseudoscalar heavy, $\tan \beta =1$, and neglect all subleading contributions to the effective potential. We find that the region of parameter space with a strong first-order phase transition requires $m_{{\tilde{q}}^{\prime }}/m_{q^{\prime }}\lesssim 1.1$ while the constraint on the lightest Higgs mass requires $m_{{\tilde{q}}^{\prime }}/m_{q^{\prime }}\gtrsim 1$ with $m_{q^{\prime }}\gtrsim 300\mathrm{GeV}$. We are led to an intriguing prediction of quarks and squarks just beyond the current Tevatron direct search limits that are poised to be discovered quickly at the LHC.

• Received 24 April 2008

DOI:https://doi.org/10.1103/PhysRevD.78.075023